Administration of epinephrine does not increase learning of fear to tone in rats anesthetized with isoflurane or desflurane

Previous reports suggest that the administration of epinephrine increases learning during deep barbiturate-chloral hydrate anesthesia in rats but not during anesthesia with 0.4% isoflurane in rabbits. We revisited this issue, using fear conditioning to a tone in rats as our experimental model for learning and memory and isoflurane and desflurane as our anesthetics. Expressed as a fraction of the minimum alveolar anesthetic concentration (MAC) preventing movement in 50% of rats, the amnestic 50% effective dose (ED(50)) for fear to tone in control rats inhaling isoflurane and injected with saline intraperitoneally (i.p.) was 0.32 +/- 0.03 MAC (mean +/- se) compared with 0.37 +/- 0.06 MAC in rats injected with 0.01 mg/kg of epinephrine i.p. and 0.38 +/- 0.03 MAC in rats injected with 0.1 mg/kg of epinephrine i.p. For desflurane, the amnestic ED(50) were 0.32 +/- 0.05 MAC in control rats receiving a saline injection i.p. versus 0.36 +/- 0.04 MAC in rats injected with 0.1 mg/kg of epinephrine i.p. We conclude that exogenous epinephrine does not decrease amnesia produced by inhaled isoflurane or desflurane, as assessed by fear conditioning to a tone in rats.